Nearly 11,000 could be at risk of HIV and hepatitis. (AAP/file)

Nearly 11,000 could be at risk of HIV and hepatitis. (AAP/file)

Up to 11,000 dental patients may have been exposed to a range of infectious diseases because of poor hygiene practices at four Sydney clinics.

NSW Health has found breaches of infection control as a result of poor cleaning and equipment sterilisation at practices at Campsie in Sydney's southwest and in Sussex Street in the city.

Authorities are also contacting patients of another dentist who runs practices in Surry Hills and Bondi Junction, media outlets are reporting.

NSW Health is contacting patients and Dr Jeremy McAnulty, the director of Health Protection at NSW Health will address media on Thursday morning.

There is a small possibility that those who had invasive procedures at the surgeries could have been infected with hepatitis B, hepatitis C and HIV.